Low birth weight infants are at risk of iron deficiency (ID), which is associated with impaired nervous system development and may lead to prolonged auditory brainstem response (ABR) latencies. We hypothesized that iron supplementation shortens ABR latencies in marginally low birth weight (MLBW, 2000-2500g) infants. In a randomized, controlled trial, 285 healthy MLBW infants received 0, 1, or 2 mg iron/kg/day of iron supplements from six weeks to six months of age. ABR absolute wave V latencies and central conduction time (CCT) were measured at the endpoint. There were no significant differences between groups in ABR wave V latencies (n=218). Furthermore, there were no significantly prolonged ABR latencies in infants with ID (n=32). CCT was significantly higher in the 2 mg-group than in the placebo-group (n=126). However, there were no significant correlations between CCT and iron intake or any iron status variable, suggesting that differences in CCT were not caused by iron. We conclude that iron supplements did not improve ABR latencies and iron deficient MLBW infants did not have impaired ABR latencies at six months, suggesting that ABR is not a sensitive measure of impaired neurological development or that mild/moderate ID causes no such impairment in MLBW infants. ABBREVIATIONS: